Page No 243:

Question 2:

Answer:

A
good fuel produces a huge amount of heat on
burning, does not produce a lot of smoke, and is easily available.

Page No 243:

Question 3:

If you
could use any source of energy for heating your food, which one would
you use and why?

Answer:

Natural
gas can be used for heating and cooking
food because it is a clean source of energy. It does not produce huge
amount of smoke on burning. Although it is highly inflammable, it is
easy to use, transport, and it produces a huge amount of heat on
burning.

Page No 248:

Question 1:

What are
the disadvantages of fossil fuels?

Answer:

The
disadvantages of fossil fuels are as
follows:

(a) Burning of coal and
petroleum produces a lot of pollutants causing air pollution.

Page No 248:

Question 2:

Why are we looking at alternate sources of energy?

Answer:

Fossil
fuels, which have been traditionally used by human beings as an
energy sources, are non-renewable sources of energy. These sources of
energy are limited and cannot replenish on their own. They are being
consumed at a large rate. If this rate of consumption continues, then
the fossil fuels would be exhausted from the Earth. Therefore, we
have to conserve the energy sources. Hence, we should look for
alternate sources of energy.

Page No 248:

Question 3:

How has
the traditional use of wind and water energy been modified for our
convenience?

Answer:

Traditionally,
waterfalls were used as a source of potential energy which was
converted to electricity with the help of turbines. Since waterfalls
are few in number, water dams have been constructed in large numbers.
Nowadays, hydro-dams are used in order to harness potential energy of
stored water. In water dams, water falls from a height on the
turbine, which produces electricity.

Earlier,
the windmills were used to harness wind energy to do mechanical work
such as lifting/drawing water from a well. Today, windmills are used
to generate electricity. In windmills, the kinetic energy of wind is
harnessed and converted into electricity. The rotatory motion of the
blades turns the turbine of the electric generator to generate
electricity.

Page No 253:

Question 1:

Can any source of energy be pollution-free? Why or why not?

Answer:

No
source of energy can be pollution-free. It
is considered that solar cells are pollution-free. However, even
their making causes environmental damage indirectly.

Also,
in the case of nuclear energy, there is no waste produced after the
fusion reactions. However, it is not totally pollution-free. To start
the fusion reactions, approximately 107
K temperature is required, which is provided by fission reactions.
The wastes released from fission reactions are very hazardous. Hence,
no source of energy is pollution-free.

Page No 253:

Question 2:

Hydrogen
has been used as a rocket fuel. Would you consider it a cleaner fuel
than CNG? Why or why not?

Answer:

Hydrogengas is cleaner than CNG. CNG contains
hydrocarbons. Therefore, it has carbon contents. Carbon is a form of
pollutant present in CNG. On the other hand, hydrogen is waste-free.
The fusion of hydrogen does not produce any waste. Hence, hydrogen is
cleaner than CNG.

Page No 253:

Question 3:

What is geothermal energy?

Answer:

Geothermal
power plants use heat of the Earth to generate electricity. This heat
energy of the Earth is known as geothermal energy.

When
there are geological changes, the molten
rocks present in the core of the earth are pushed to the earth’s
crust. This forms regions of hot spot. Steam is generated when the
underground water comes in contact with these hot spots forming hot
springs. This trapped steam is used to generate electricity in the
geothermal power plants.

Page No 253:

Question 4:

What are the advantages of nuclear energy?

Answer:

The advantages of nuclear energy are
as follows:

(a) Large
amount of energy is produced per unit mass.

(b) It
does not produce smoke. It is a clean energy.

(c) Fission of one atom of uranium produces 10
million times the energy released by
burning of one atom of carbon.

(d) Fusion of four hydrogen atoms produces huge
amount of energy approximately equal to 27 MeV.

Page No 254:

Question 1:

A solar
water heater cannot be used to get hot water on

(a) a
sunny day (b) a cloudy day

(c) a hot
day (d) a windy day

Answer:

(b) A solar water heater uses solar energy to heat water. It requires
bright and intense sunlight to function properly. On a cloudy day,
the sunlight reflects back in the sky from the clouds and is unable
to reach the ground. Therefore, solar energy is not available for the
solar heater to work properly. Hence, solar water heater does not
function on a cloudy day.

Page No 254:

Question 2:

Give the
names of two energy sources that you would consider to be
exhaustible. Give reasons for your choices.

Answer:

Two
exhaustible energy sources are as follows:

(a) Coal: It is produced
from dead remains of plants and animals that remain buried under the
earth’s crust for millions of years. It takes millions of years
to produce coal. Industrialization has increased the demand of coal.
However, coal cannot replenish within a short period of time. Hence,
it is a non-renewable or exhaustible source of energy.

(b) Wood: It is obtained from forests.
Deforestation at a faster rate has caused a reduction in the number
of forests on the Earth. It takes hundreds of years to grow a forest.
If deforestation is continued at this rate, then there would be no
wood left on the Earth. Hence, wood is an exhaustible source of
energy.

Page No 255:

Question 2:

Which of
the following is not an example of a bio-mass energy source?

(a) wood

(b) gobar
gas

(c) nuclear energy

(d) coal

Answer:

(c) Bio-mass is a source of energy that is obtained from plant
materials and animal wastes. Nuclear energy is released during
nuclear fission and fusion. In nuclear fission, uranium atom is
bombarded with low-energy neutrons. Hence, uranium atom splits into
two relatively lighter nuclei. This reaction produces huge amount of
energy. In nuclear fusion reaction, lighter nuclei are fused together
to form a relatively heavier nuclei. This reaction produces
tremendous amount of energy. Hence, nuclear energy is not an example
of bio-mass energy source.

Wood
is a plant material, gobar
gas is formed from animal dung, and coal is a fossil fuel obtained
from the buried remains of plants and animals. Hence, these are
bio-mass products.

Page No 255:

Question 3:

Most of
the sources of energy we use represent stored solar energy. Which of
the following is not ultimately derived from the Sun’s energy?

(a)
Geothermal energy

(b)
Wind energy

(c)
Nuclear energy

(d)
Bio-mass

Answer:

(c) Nuclear energy is released during nuclear fission and fusion. In
nuclear fission, uranium atom is bombarded with low-energy neutrons.
Hence, uranium atom splits into two relatively lighter nuclei. This
reaction produces huge amount of energy. In nuclear fusion reaction,
lighter nuclei are fused together to form a relatively heavier
nuclei. The energy required to fuse the lighter nuclei is provided by
fission reactions. This reaction produces tremendous amount of
energy. These reactions can be carried out in the absence or presence
of sunlight. There is no effect of sunlight on these reactions.
Hence, nuclear energy is not ultimately derived from Sun’s
energy.

Geothermal
energy, wind energy, and bio-mass are all ultimately derived from
solar energy.

Geothermal
energy is stored deep inside the earth’s crust in the form of
heat energy. The heating is caused by the absorption of atmospheric
and oceanic heat. It is the sunlight that heats the atmosphere and
oceans.

Wind energy is harnessed from the blowing of winds. The uneven
heating of the earth’s surface by the Sun causes wind.

Bio-mass is derived from dead plants and animal wastes. Chemical
changes occur in these dead plants and animal wastes in the presence
of water and sunlight. Hence, bio-mass is indirectly related to
sunlight.

Page No 255:

Question 4:

Compare
and contrast fossil fuels and the Sun as direct sources of energy.

Answer:

Fossil
fuels are energy sources, such as coal and petroleum, obtained from
underneath the Earth’s crust. They are directly available to
human beings for use. Hence, fossil fuels are the direct source of
energy. These are limited in amount. These are non-renewable sources
of energy because these cannot be replenished in nature. Fossil fuels
take millions of years for their formation. If the present fossil
fuel of the Earth gets exhausted, its formation will take several
years. Fossil fuels are also very costly.

On the
other hand, solar energy is a renewable and direct source of energy.
The Sun has been shining for several years and will do so for the
next five billion years. Solar energy is available free of cost to
all in unlimited amount. It replenishes in the Sun itself.

Page No 255:

Question 5:

Compare and contrast bio-mass and hydro electricity as sources of
energy.

Answer:

Bio-mass
and hydro-electricity both are renewable sources of energy. Bio-mass
is derived from dead plants and animal wastes. Hence, it is naturally
replenished. It is the result of natural processes. Wood, gobar
gas, etc. are some of the examples of bio-mass.

Hydro-electricity,
on the other hand, is obtained from the potential energy stored in
water at a height. Energy from it can be produced again and again. It
is harnessed from water and obtained from mechanical processes.

Page No 255:

Question 6:

What are the limitations of extracting energy from −

(a) the
wind? (b) waves? (c) tides?

Answer:

(a) Wind energy is harnessed by windmills. One of the limitations of
extracting energy from wind is that a windmill requires wind of speed
more than 15 km/h to generate electricity. Also, a large number of
windmills are required, which covers a huge area.

(b) Very strong ocean waves are required in order to extract energy
from waves.

(c) Very high tides are required in order to extract energy from
tides. Also, occurrence of tides depends on the relative positions of
the Sun, moon, and the Earth.

Page No 255:

Question 7:

On what basis would you classify energy sources as

(a) renewable
and non-renewable?

(b) exhaustible
and inexhaustible?

Are the
options given in (a) and (b) the same?

Answer:

(a) The source of energy that replenishes in nature is known as
renewable source of energy. Sun, wind, moving water, bio-mass, etc.
are some of the examples of renewable sources of energy.

The source of energy that does not replenish in nature is known as
non-renewable source of energy. Coal, petroleum, natural gas, etc.
are some of the examples of non-renewable sources of energy.

(b) Exhaustible sources are those sources of energy, which will
deplete and exhaust after a few hundred years. Coal, petroleum, etc.
are the exhaustible sources of energy.

Inexhaustible resources of energy are those sources, which will not
exhaust in future. These are unlimited. Bio-mass is one of the
inexhaustible sources of energy.

Yes.
The options given in (a) and (b) are the
same.

Page No 255:

Question 8:

What are the qualities of an ideal source of energy?

Answer:

An ideal source of energy must be:

I. Economical

II. Easily
accessible

III. Smoke/pollution
free

IV. Easy
to store and transport

V. Able
to produce huge amount of heat and energy on burning

Page No 255:

Question 9:

What are
the advantages and disadvantages of using a solar cooker? Are there
places where solar cookers would have limited utility?

Answer:

Solar
cooker uses Sun’s energy to heat and cook food. It is
inexhaustible and clean renewable source of energy. It is free for
all and available in unlimited amount. Hence, operating a solar
cooker is not expensive.

Disadvantage
of a solar cooker is that it is very expensive. It does not work
without sunlight. Hence, on cloudy day, it becomes useless.

The places
where the days are too short or places with cloud covers round the
year, have limited utility for solar cooker.

Page No 255:

Question 10:

What are
the environmental consequences of the increasing demand for energy?
What steps would you suggest to reduce energy consumption?

Answer:

Industrialization
increases the demand for energy. Fossil fuels are easily accessible
sources of energy that fulfil this demand.
The increased use of fossil fuels has a harsh effect on the
environment. Too much exploitation of fossil fuels increases the
level of green house gas content in the atmosphere, resulting in
global warming and a rise in the sea level.

It is not
possible to completely reduce the consumption of fossil fuels.
However, some measures can be taken such as using electrical
appliances wisely and not wasting electricity. Unnecessary usage of
water should be avoided. Public transport system with mass transit
must be adopted on a large scale. These small steps may help in
reducing the consumption of natural resources and conserving them.